Active phased array antenna

ABSTRACT

A plurality of reception modules ( 1   a,   1   b ) receive signals from a plurality of antennas ( 2   a,   2   b ) respectively. A synthesizer ( 3 ) synthesizes output signals of the plurality of reception modules ( 1   a,   1   b ). Each of the plurality of reception modules ( 1   a,    1   b ) includes a first sample-and-hold circuit ( 7   a,   7   b ) sampling and holding a received signal, a second sample-and-hold circuit ( 8   a,   8   b ) sampling and holding an output signal of the first sample-and-hold circuit ( 7   a,   7   b ), and a controller ( 9   a,   9   b ) controlling a timing at which the first sample-and-hold circuit ( 7   a,   7   b ) samples and holds the signal. Operation timings of the first sample-and-hold circuits ( 7   a,   7   b ) are set for the respective reception modules ( 1   a,   1   b ). Operation timings of the second sample-and-hold circuits ( 8   a,   8   b ) of the plurality of reception modules ( 1   a,   1   b ) are same.

FIELD

The present invention relates to an active phased array antenna configured to receive electromagnetic wave through a plurality of antennas.

BACKGROUND

A phased array antenna enables electronical scanning of a radio wave beam by controlling the phases of radio frequency (RF) signals received from a plurality of antennas. A phased array antenna in which an active circuit such as an amplification circuit is placed between each antenna and a phase device is called an active phased array antenna. In the active phased array antenna, the phase of a signal received from each antenna is controlled by the phase device, and the signals are synthesized by a synthesizer.

Practically, to control the phase of a received signal in a phased array antenna, the group delay of the received signal needs to be controlled. In a case of a line spectrum signal with no frequency band, a phase difference and a group delay difference may completely match. However, with a wider frequency band of a signal, although a beam of the signal at the band center is accurately radiated in a set direction, error occurs to the angle of radiation for a signal at a band edge. The influence is significant in a case of an antenna having a large aperture or a signal having a wide frequency band. To solve this problem, a technology providing a delay time difference to sampling clocks of an AD converter and a DA converter has been proposed (refer to PTL 1, for example).

CITATION LIST Patent Literature

-   [PTL 1] Japanese Patent No. 4533572

SUMMARY Technical Problem

In the conventional technology, received signals are synthesized by digital calculation. In a case of a large antenna aperture size, which leads to a significant error in phase control, there is a large number of antennas, resulting in a significantly large number of buses through which digital signals are transmitted. Thus, this may not be feasible in some cases due to constraint on a substrate design or the number of terminals of an IC configured to perform digital calculation. In addition, in a case of a wide signal frequency band, the data rate is high because the Nyquist frequency of an AD converter is high, and thus this may not be feasible in some cases due to the processing capacity of an IC configured to perform digital calculation.

An object of the present invention, which has been made to solve the problem as described above, is to provide an active phased array antenna capable of controlling a delay time without performing digital synthesis arithmetic processing.

Solution to Problem

An active phased array antenna according to the present disclosure includes: a plurality of antennas; a plurality of reception modules receiving signals from the plurality of antennas respectively; and a synthesizer synthesizing output signals of the plurality of reception modules, wherein each of the plurality of reception modules includes a first sample-and-hold circuit sampling and holding a received signal, a second sample-and-hold circuit sampling and holding an output signal of the first sample-and-hold circuit, and a controller controlling a timing at which the first sample-and-hold circuit samples and holds the signal, operation timings of the first sample-and-hold circuits are set for the respective reception modules, and operation timings of the second sample-and-hold circuits of the plurality of reception modules are same.

Advantageous Effects of Invention

In the present disclosure, the operation timing of the first sample-and-hold circuits configured to sample and hold received signals are set for the respective reception modules, the operation timings of the second sample-and-hold circuits configured to sample and hold output signals of the first sample-and-hold circuits are same between the plurality of reception modules, and output signals of the plurality of reception modules are synthesized. Accordingly, a delay time can be controlled without performing digital synthesis arithmetic processing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an active phased array antenna according to Embodiment 1.

FIG. 2 is a block diagram illustrating each sample-and-hold circuit according to Embodiment 1.

FIG. 3 is a diagram illustrating the operation timing of a reception module.

FIG. 4 is a diagram illustrating the operation timing of a reception module.

FIG. 5 is a diagram illustrating an output signal of the synthesizer.

FIG. 6 is a block diagram illustrating an active phased array antenna according to Embodiment 2.

FIG. 7 is a block diagram illustrating an FIR filter.

FIG. 8 is a timing chart illustrating the operation of an FIR filter.

DESCRIPTION OF EMBODIMENTS

An active phased array antenna according to the embodiments of the present disclosure will be described with reference to the drawings. The same components will be denoted by the same symbols, and the repeated description thereof may be omitted.

Embodiment 1

FIG. 1 is a block diagram illustrating an active phased array antenna according to Embodiment 1. A plurality of reception modules 1 a and 1 b receive signals from a plurality of antennas 2 a and 2 b, respectively. A synthesizer 3 synthesizes output signals of the plurality of reception modules 1 a and 1 b. An AD converter 4 converts a signal obtained through the synthesis by the synthesizer 3 into digital data.

The reception module 1 a includes a low noise amplifier 5 a, a frequency conversion unit 6 a, a first sample-and-hold circuit 7 a, a second sample-and-hold circuit 8 a, and a phase shifter 9 a. The low noise amplifier 5 a amplifies the electrical power of a signal received from the corresponding antenna 2 a. The frequency conversion unit 6 a converts the frequency of the amplified signal from a carrier wave band into a frequency band that can be AD converted. The first sample-and-hold circuit 7 a samples and holds the frequency-converted signal in accordance with an input clock. The second sample-and-hold circuit 8 a samples and holds an output signal of the first sample-and-hold circuit 7 a. The phase shifter 9 a controls a timing at which the first sample-and-hold circuit 7 a samples and holds the signal.

Similarly, the reception module 1 b includes a low noise amplifier 5 b, a frequency conversion unit 6 b, a first sample-and-hold circuit 7 b, a second sample-and-hold circuit 8 b, and a phase shifter 9 b. Each component has a function same as that in the reception module 1 a.

A local oscillator LO generates a local oscillation signal for the frequency conversion of each of the frequency conversion units 6 a and 6 b. The phase shift amount of each of the phase shifters 9 a and 9 b is smaller than ±90°. A sampling clock source SCLK generates a sampling clock for driving the first sample-and-hold circuits 7 a and 7 b and the second sample-and-hold circuits 8 a and 8 b. However, the operation timings of the first sample-and-hold circuits 7 a and 7 b are set for the respective reception modules 1 a and 1 b by the phase shifters 9 a and 9 b, but the operation timings of the second sample-and-hold circuits 8 a and 8 b of the plurality of reception modules 1 a and 1 b are same.

FIG. 2 is a block diagram illustrating each sample-and-hold circuit according to Embodiment 1. The first sample-and-hold circuits 7 a and 7 b and the second sample-and-hold circuits 8 a and 8 b each include switches 10 and 11, capacitors 12 and 13, and voltage followers 14 and 15. Input voltage is sampled when the switch 10 is short-circuited, and the input voltage is held by the capacitor 12 when the switch 10 is opened. The held voltage is sampled-and-held by a capacitor 13 through a switch 11 configured to operate at polarity opposite to that of the switch 10 and through the voltage follower 14, and is output through the voltage follower 15.

The following describes the operation of the active phased array antenna according to the present embodiment. FIGS. 3 and 4 are each a diagram illustrating the operation timing of a reception module. FIG. 3 illustrates the operation timing of the reception module 1 a, and FIG. 4 illustrates the operation timing of the reception module 1 b. FIG. 5 is a diagram illustrating an output signal of the synthesizer.

Signal electromagnetic waves radiated and propagated from the outside are transferred to the reception modules 1 a and 1 b through the antennas 2 a and 2 b, respectively. Signals amplified and frequency-converted in the modules are input to the first sample-and-hold circuits 7 a and 7 b.

A sampling clock having a period Ts is supplied from the sampling clock source SCLK. The phase shifters 9 a and 9 b each shift the phase of the sampling clock. The first sample-and-hold circuits 7 a and 7 b each sample the voltage of a signal at a rising edge of the sampling clock output from the corresponding one of the phase shifters 9 a and 9 b, and maintains a zero-th hold waveform until the next rising edge. A control circuit 16 sets the amounts of phase shift by the phase shifters 9 a and 9 b for the respective modules so that a desired antenna face can be obtained after synthesis. In this example, the phase shift amount of the phase shifter 9 a is 0°, and the phase amount of the phase shifter 9 b is ϕ°. In this case, the first sample-and-hold circuit 7 b performs signal sampling and holding at a timing delayed behind the first sample-and-hold circuit 7 a by Td=Ts·ϕ/360.

The second sample-and-hold circuits 8 a and 8 b each sample and hold an output signal of the corresponding one of the first sample-and-hold circuits 7 a and 7 b at a falling edge of the sampling clock. The synthesizer 3 adds and synthesizes output signals of the second sample-and-hold circuits 8 a and 8 b of the plurality of reception modules 1 a and 1 b. The AD converter 4 converts an output signal of the synthesizer 3 into a digital signal.

As described above, the first sample-and-hold circuit 7 b performs sampling and holding at the timing delayed behind the first sample-and-hold circuit 7 a by Td. Thus, the synthesis of output signals of the reception modules 1 a and 1 b by the synthesizer 3 is equivalent to signal delay of Td relative to the reception module 1 b by the reception module 1 a.

As described above, in the present embodiment, the operation timings of the first sample-and-hold circuits 7 a and 7 b configured to sample and hold received signals are set for the respective reception modules 1 a and 1 b, the operation timings of the second sample-and-hold circuits 8 a and 8 b configured to sample and hold output signals of the first sample-and-hold circuits 7 a and 7 b are same between the plurality of reception modules 1 a and 1 b, and output signals of the plurality of reception modules 1 a and 1 b are synthesized. Accordingly, a delay time can be controlled without performing digital synthesis arithmetic processing. Thus, there is no need to provide a large number of signal bus wires, and a lightweight and compact active phased array antenna with low electric power consumption can be obtained. This active phased array antenna can be achieved even in a case of a large antenna aperture size and a wide signal frequency band.

In addition, the operation timings of the first sample-and-hold circuits 7 a and 7 b can be easily controlled by setting the amounts of phase shift by the phase shifters 9 a and 9 b configured to shift the phase of the sampling clock in the first sample-and-hold circuits 7 a and 7 b.

Embodiment 2

FIG. 6 is a block diagram illustrating an active phased array antenna according to Embodiment 2. In the present embodiment, the first sample-and-hold circuits 7 a and 7 b each directly sample and hold a carrier wave band signal and simultaneously perform frequency conversion and sampling-holding. FIR filters 17 a and 17 b are rate converters configured to perform rate conversion of the sampling rates of output signals of the respective first sample-and-hold circuits 7 a and 7 b, and remove unnecessary signals while decreasing the sampling rates and maintaining the linearity of phase shift.

The phase shifters 9 a and 9 b shift the phase of the local oscillation signal to generate sampling clocks of the respective first sample-and-hold circuits 7 a and 7 b. The local oscillation signal has an extremely high frequency relative to a signal bandwidth and thus is converted to a necessary and sufficient sampling rate to facilitate the following circuit processing. The phase shifters 9 a and 9 b also function as local oscillator for the frequency conversion of the first sample-and-hold circuits 7 a and 7 b. Frequency dividers 18 a and 18 b generate sampling clocks common to the second sample-and-hold circuits 8 a and 8 b by dividing the local oscillation signal to rates same as those of the FIR filters 17 a and 17 b.

FIG. 7 is a block diagram illustrating an FIR filter. This FIR filter is a moving-average filter with four taps. A plurality of sample-and-hold circuits 19 a to 19 d sample and hold input signals. An adder 20 adds output signals of the plurality of sample-and-hold circuits 19 a to 19 d. A sample-and-hold circuit 21 samples and holds an output signal of the adder 20. A clock control circuit 22 generates a sampling clock for driving the sample-and-hold circuits 19 a to 19 d and 21.

FIG. 8 is a timing chart illustrating the operation of an FIR filter. A signal having a period four times longer than the clock of five local oscillation signals and having a duty of 25% is output from the clock control circuit. The sample-and-hold circuits 19 a to 19 d sample and hold input signals at four timings different from one another. When the four sample-and-hold circuits 19 a to 19 d all complete the sampling and holding, the sample-and-hold circuit 21 outputs an output signal of the adder 20. Since the pieces of sample-and-hold data of the four timings are added, the output result is a moving average, and the FIR filter has a low-pass characteristic. Simultaneously, the sampling rate is converted to 1/4 of the original rate.

The following describes the operation of the active phased array antenna according to the present embodiment. Signal electromagnetic waves radiated and propagated from the outside are transferred to the reception modules 1 a and 1 b through the antennas 2 a and 2 b, respectively. Signals amplified in the modules are input to the first sample-and-hold circuits 7 a and 7 b. The first sample-and-hold circuits 7 a and 7 b each perform sampling and holding based on a sampling clock obtained by shifting a local oscillation signal at the corresponding one of the phase shifters 9 a and 9 b, and simultaneously perform frequency conversion. In this case, when the phase shift amount of the phase shifter 9 a is 0° and the phase amount of the phase shifter 9 b is φ°, the first sample-and-hold circuit 7 b performs signal sampling and holding at a timing delayed behind the first sample-and-hold circuit 7 a by Td=Ts·ϕ/360. An output signal of each of the first sample-and-hold circuits 7 a and 7 b is sampled-and-held by the corresponding one of the second sample-and-hold circuits 8 a and 8 b at a falling timing of the sampling clock and then output.

Similarly to Embodiment 1, the first sample-and-hold circuit 7 b performs sampling and holding at a timing delayed behind the first sample-and-hold circuit 7 a by Td. Thus, the synthesis of output signals of the reception modules 1 a and 1 b by the synthesizer 3 is equivalent to signal delay of Td relative to the reception module 1 b by the reception module 1 a. Accordingly, a delay time can be controlled without performing digital synthesis arithmetic processing.

In the present embodiment, the first sample-and-hold circuits 7 a and 7 b perform signal frequency conversion and sampling-holding, and the FIR filters 17 a and 17 b perform rate conversion of the sampling rates of output signals of the first sample-and-hold circuits 7 a and 7 b. Accordingly, signal lines for the frequency conversion units 6 a and 6 b and the sampling clock source SCLK are unnecessary, and thus a smaller-sized active phased array antenna can be achieved. In addition, the FIR filters 17 a and 17 b can remove any unnecessary signal while performing rate conversion of the sampling rates.

REFERENCE SIGNS LIST

-   1 a, 1 b reception module; 2 a, 2 b antenna; 3 synthesizer; 7 a, 7 b     first sample-and-hold circuit; 8 a, 8 b second sample-and-hold     circuit; 9 a, 9 b phase shifter (controller); 17 a, 17 b FIR filter     (rate converter) 

1. An active phased array antenna comprising: a plurality of antennas; a plurality of reception modules receiving signals from the plurality of antennas respectively; and a synthesizer synthesizing output signals of the plurality of reception modules, wherein each of the plurality of reception modules includes a first sample-and-hold circuit sampling and holding a received signal, a second sample-and-hold circuit sampling and holding an output signal of the first sample-and-hold circuit, and a controller controlling a timing at which the first sample-and-hold circuit samples and holds the signal, operation timings of the first sample-and-hold circuits are set for the respective reception modules, and operation timings of the second sample-and-hold circuits of the plurality of reception modules are same.
 2. The active phased array antenna according to claim 1, wherein the controller includes a phase shifter shifting a phase of a sampling clock of the first sample-and-hold circuit.
 3. The active phased array antenna according to claim 1, wherein the first sample-and-hold circuit performs frequency conversion and sampling-holding of the signal, and the reception module includes a rate converter performing rate conversion of a sampling rate of an output signal of the first sample-and-hold circuit.
 4. The active phased array antenna according to claim 3, wherein the rate converter includes an FIR filter.
 5. The active phased array antenna according to claim 2, wherein the first sample-and-hold circuit performs frequency conversion and sampling-holding of the signal, and the reception module includes a rate converter performing rate conversion of a sampling rate of an output signal of the first sample-and-hold circuit.
 6. The active phased array antenna according to claim 5, wherein the rate converter includes an FIR filter. 